Morphology and magnetic properties of pressed barium hexaferrite BaFe₁₂O₁₉ materials

Barium hexaferrite tablets were compacted at pressures of 50-149 kN/cm² and subsequently calcined at different temperatures up to 1350 °C for various durations. The compaction pressure has a non-monotonic influence on the calcined sample density and coercivity. The apparent density shows a maximum concomitant to a minimum in coercivity near a compaction pressure of 120 kN/cm². In contrast the Curie temperature of 459 °C are not influenced by the compaction pressure. The optimized compaction pressure and subsequent calcination temperature for obtaining high-density single phase material is inferred to 108 kN/cm² and 1350 °C, respectively. The resulting pellets show surfaces of two different sized crystallites in the 3-10 μm and 50-150 μm ranges and grains with cheese-like pores of 5-7 μm in the interior. The interior grain size increases with compaction pressure to up to 150-250 μm, while the pore size stays unaffected.